With recent diffusion of electric vehicles, there is an increasing need for a charging device capable of quickly charging a high-capacity in-vehicle battery in a short period of time such as about ten minutes.
Normally, such a charging device converts an alternating-current voltage, which is supplied externally, into a direct-current voltage by rectification and smoothing, and thereafter the device generates charging power at a desired voltage value by a converter portion stepping up or down the direct-current voltage, and outputs the power to the in-vehicle battery, thereby charging the in-vehicle battery.
Conventionally, various charging devices for in-vehicle batteries are under study, and in general, the charging voltage is set at a desired value through PWM control by which the duty cycle of a switching element included in the converter portion is changed on the basis of the value of the charging voltage, as in Patent Documents 1 and 2.